Someone had to decide which lens should be released in what order. That order is based on Fuji's perception of the market; that's it. Personally, I see a lot of forethought going in to which lens makes the most sense to release from a Customer point of view.

They have a limited number of designers developing the prototypes. When they get a good idea of when a model will be ready to release, they put it on the Roadmap. Right now, Fuji's scrambling to put out enough X-T1's and XF 10-24mm's to fill the existing backorders.